1:45 PM - 2:00 PM
▲ [14p-E206-1] Ionic Liquid Gating of Metal Contacts: Effect of Cation Size
Keywords:ionic liquid
Electric-double-layer (EDL) gating with ionic liquids has been attracting considerable interests owing to its tremendous gating power.1 Since the EDL formed at liquid/solid interfaces functions as a huge capacitance and can induce large charge accumulation, it is used for gating not only organic materials, oxides, and semiconductors, but also metal systems.2
In this work, we have used a liquid-gated EDL transistor geometry for gold nanojunctions to control the conductance of metal contacts. The ionic liquid we used was DEME-TFSI. Figure 1(a) shows the VG-dependence of the conductance of a gold junction when G ~ 100G0, where G0 º 2e2/h. The conductance of the gold junction increases with increasing VG from 0V, but the conductance increase saturates for VG > 1 V. Furthermore, hysteresis appears when the gate voltage is swept up and down. Figure 1(b) plots the capacitance of the sample as a function of VG. The curve shows only one peak for the sweep-up but two peaks appear for the sweep-down. This behavior is attributed to a geometrical reason: since the ionic structure of a DEME cation can be viewed as a charged head with a neutral tails (while a TFSI anion is regarded as a single charged bead) (Fig. 1(c)), these neutral beads play the role of latent voids that can cause reorientations of the ions3 and causes different ion arrangement for sweep-up and down. This result gives a new insight when EDL gating is used for atomic scale systems. In the presentation, comparison with another kind of cation will also be presented.
In this work, we have used a liquid-gated EDL transistor geometry for gold nanojunctions to control the conductance of metal contacts. The ionic liquid we used was DEME-TFSI. Figure 1(a) shows the VG-dependence of the conductance of a gold junction when G ~ 100G0, where G0 º 2e2/h. The conductance of the gold junction increases with increasing VG from 0V, but the conductance increase saturates for VG > 1 V. Furthermore, hysteresis appears when the gate voltage is swept up and down. Figure 1(b) plots the capacitance of the sample as a function of VG. The curve shows only one peak for the sweep-up but two peaks appear for the sweep-down. This behavior is attributed to a geometrical reason: since the ionic structure of a DEME cation can be viewed as a charged head with a neutral tails (while a TFSI anion is regarded as a single charged bead) (Fig. 1(c)), these neutral beads play the role of latent voids that can cause reorientations of the ions3 and causes different ion arrangement for sweep-up and down. This result gives a new insight when EDL gating is used for atomic scale systems. In the presentation, comparison with another kind of cation will also be presented.